FIG. 1 is an example of a communications private line deployed by an operator for an enterprise. A customer A and a customer B are two branch networks of an enterprise. The customer A is connected through customer premises equipment (CPE) A to a metropolitan area access network A provided by the operator. The customer B is connected through CPE B to a metropolitan area access network B provided by the operator. The metropolitan area access network A and the metropolitan area access network B are connected through provider edge (PE) devices to a core network, and communicate with each other by using the core network.
A metropolitan area access network provides operator-committed bandwidth. For example, as shown in FIG. 1, the operator-committed bandwidth is 20 Mbps. The operator may send test data to the metropolitan area access network to test whether bandwidth of the metropolitan area access network reaches the committed bandwidth. However, such a manner can be applied only before the metropolitan area access network transmits service data of the enterprise. If the metropolitan area access network has begun transmitting the service data of the enterprise, the test data occupies bandwidth of the service data, and consequently, normal operation of an enterprise service is affected.